Smart transparent surfaces for energy-efficient buildings: enabling 5G mmWave connectivity with multispectral compatibility

This paper presents a glass-penetrating transparent surface (GPTS) that provides multispectral compatibility across visible light (VIS), infrared (IR), and ultraviolet (UV) bands, while improving transmission in the 5G millimeter-wave (mmWave) band. For building applications, these techniques are critical to efficiently deploy on-premises mmWave fixed wireless access (FWA) as well as wireless communications with outdoor-to-indoor and indoor-to-outdoor connectivity. To optimize transmission and angular stability, various frequency-selective surface (FSS) designs based on a metallic layer (ML) on glass (GPTS-ML) are first investigated. The ML was then replaced with two types of advanced transparent coatings PEI/Ag/PEDOT: PSS: a transparent electrode (TE) and a low-E (LE) coating with sheet resistances of 9.2 Ω/sq and 5 Ω/sq, respectively. Both structures achieve a transmission loss below 4.7 dB at 28 GHz, while maintaining high VIS transmittance ($$\:{T}_{vis}$$) and simultaneously reducing IR transmittance ($$\:{T}_{IR}$$) and UV transmittance ($$\:{T}_{UV}$$). GPTS-TE provides $$\:{T}_{vis}$$ of approximately 66% with balanced $$\:{T}_{UV}$$ of 40% and $$\:{T}_{IR}$$ of 44%, whereas GPTS-LE exhibits stronger IR/UV blocking, with $$\:{T}_{IR}$$ of 19% and $$\:{T}_{UV}$$ of 29.5%, while sustaining low-loss mm-wave transmission. These results illustrate a path towards multi-spectral surface applications that simultaneously support energy efficiency, user comfort, and next generation 5G mmWave FWA services. Our work highlights the potential of transparent metasurfaces as a foundational element in smart buildings and urban communications infrastructure, thereby enabling sustainable and connected living environments.